Well, the fourth is weird anyway. :)
I bought this for my eldest fat cat, but ended giving it twice a day to 3 of my cats, including the youngest one. Not sure what it contains that makes them crazy, it's enough to open the bag and they appear from nowhere, mouth open.
Yes, the fat old one does jump more than before. It does not make his age disappear, but he can now climb the window without much fuss.